1. Field of the Invention
The present invention relates to a method of smoothing image data.
2. Description of the Prior Art
Various methods of smoothing image data have heretofore been known in the art for decreasing or eliminating fluctuations or noise in image data. Study on data compression (highly efficient data coding) for efficient transmission and recording of image data has made much progress in recent years. In such data compression, the data smoothing is employed as a pretreatment process to increase a data compression efficiency. More specifically, by smoothing image data in predictive coding, the differential is reduced and the number of codes therefor may be reduced, and by smoothing image data in orthogonal transform coding, the converted data is concentrated in a low-frequency range. Therefore, the region in which the code length may be short is widened, and hence the data compression rate may be increased.
Among image data smoothing methods which are often employed normally are mean smoothing and median smoothing. According to the mean smoothing process, the image data of each pixel of a two-dimensional image is replaced with the mean value of data of a plurality of pixels (pixels within a mask size) including the pixel to be replaced. In the median smoothing method, the median value of each data item is used instead of the mean value in the above replacement process.
With the mean and median smoothing methods, those areas in which image data variations are large and small are uniformly smoothed. Therefore, if a high data smoothing effect were to be obtained, the area with a small image data variation would be excessively smoothed, thus losing image details. If such a difficulty were to be avoided, the area with a large image data variation would not sufficiently be smoothed. Any large variation left in image data after it has been smoothed is responsible for the prevention of an increase in the data compression rate.